In typical Gojo fashion, the sorcerer had simply shown up and handed you a child before leaving to who knows where.

That's not true. In reality he said "here's that kid I rescued, have fun!" But it's the same thing.

So now you have a pretty angry looking kid. Or...Cold? Not happy, let's say that. He was clearly young, six maybe, and yet didn't have that childish innocence to him. Poor thing looked like he was constantly protecting himself emotionally and physically.